Let me repeat that once again, for emphasis: Japanese scientists now have a blood test to diagnose depression!

Never mind all that messy “talk-to-the-patient” stuff. And you can throw away your tired old DSM-IV, because this is the new world: biological diagnosis!! The press release describing the research even suggests that the test “could improve early detection rates of depression if performed during regular medical checkups.” That’s right: next time you see your primary doc, he or she might order—along with your routine CBC and lipid panel—an ethanolamine phosphate test. If it comes back positive, congratulations! You’re depressed!

If you can detect the skepticism in my voice, good. Because even if this “biomarker” for depression turns out to be 100% accurate (which it is not—see below), its use runs entirely against how we should be practicing person-centered (not to be confused with “personalized”) medicine. As a doctor, I want to hear your experiences and feelings, and help you with those symptoms, not run a blood test and order a drug.

[Incidentally, the Asahi press release made me chuckle when it stated: “About 90 percent of doctors base their diagnosis of depression on experience and varying factors.” What about the other 10%? Magic?]

As it turns out, I think there’s a lot to suggest that this particular blood test may not yet be ready for prime time. For one, the work has not yet been published (and deciphering scientific results from a press release is always a risky proposition). Secondly, the test was not 100% accurate; it failed to identify depression in 18% of cases, and falsely labeled healthy people as “depressed” 5% of the time. (That’s a sensitivity of 82% and a specificity of 95%, for those of you playing along at home.)

Further, what the heck is ethanolamine phosphate, and why would it be low in depressed people? Is it a chemical secreted by the “happiness centers” of the brain? Does it predict the onset or worsening of a depressive episode? Is it somehow affected by antidepressant treatment? As far as I can tell from a quick literature search, there has been no report—or even a suggestion—of ethanolamine (or any of its metabolites) being involved in the pathogenesis of mood disorders. Then again, maybe I didn’t get the Japanese translation just right.

Anyway, where this “marker” came from is anybody’s guess. It’s entirely possible (although I can’t be sure, because the Japanese group has not yet published their findings) that the researchers measured the blood levels of dozens of molecules and found the “best” results with this one. We sometimes call this a “fishing expedition.” Obviously, the finding has to be replicated, and if it was, in fact, just a lucky result, further research will bear that out.

What if he’s right? How would you feel if you went to a routine doctor’s visit next week, got an order for blood work, and a secretary called you a few days later to tell you that you have depression? Even if you don’t feel depressed?

Were there other motives for developing such a test? Probably. One of the press releases quotes the Japanese Ministry of Health as saying that “only one quarter of the people who need treatment” actually get it. So maybe this blood test is simply a way to offer treatment to more people expand the market for antidepressants—even to those who don’t want treatment. And then, of course, HMT probably wants a piece of the pie. HMT is already developing a commercial test to measure ethanolamine phosphate levels; obviously, widespread adoption of this test would translate into big bucks for HMT, indeed.

So while many other questions remain to be answered, I must say I’m not holding my breath. Biological screening tests for psychiatric disorders have no face validity (in other words, if a test is positive but a person shows no signs or symptoms, then what?) and a positive result may expose patients to “preventive” treatments that are costly and cause unwanted side effects.

In my opinion, the best way (if any) to use a biomarker is in a “confirmatory” or “rule-out” function. Is that demoralized, ruminative, potentially suicidal patient in your office simply going through a rough period in her life? Or is she clinically depressed? Will she respond to medications, or is this something that will simply “pass”? In cases like this, measuring ethanolamine phosphate (or another similar marker) might be helpful.

But I don’t think we’ll ever be able to screen for psychiatric illness the same way a primary care doc might screen for, say, breast cancer or diabetes. To do so would redefine the entire concept of “mental” illness (perhaps making it “neurological” illness instead?). It also takes the person out of the picture. At the end of the day, it’s always the patient’s thoughts, words, and experiences that count. Ignoring those—and focusing instead on a chemical in the bloodstream—would be an unfortunate path to tread.

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Steve Balt

All posts, unless otherwise noted, are written by Steve Balt, MD, current Editor-in-Chief of The Carlat Psychiatry Report (TCPR). TCPR is a monthly continuing education newsletter for psychiatrists and other mental health professionals with a focus on practical tips, clinical pearls, and reviews of research with the promise of no pharmaceutical or device industry bias. Read more about Dr. Balt on his About Me page.